1. Field of the Invention
The present invention relates to a toner and production method thereof, and a developer and image forming method using the toner.
2. Description of the Related Art
Hereto, various methods have been known as an electrophotographic method. The electrophotographic method generally a method includes forming a latent electrostatic image on a latent electrostatic image bearing member (may also be referred to as an “electrophotographic photoconductor” or “photoconductor”) by means of various units, developing the latent electrostatic image with a toner to form a visible image, transferring the visible image, if necessary, to a recording medium such as paper, and fixing the visible image onto the recording medium with heat and/or pressure to thereby provide a copy or print.
A common electrophotographic method with a full color photocopier is a method where four latent electrostatic image bearing members are used to form a latent electrostatic image on each member, latent electrostatic images are respectively developed with a cyan toner, magenta toner, yellow toner, and black toner, the resulting toner images are transferred to a recording medium, which is conveyed on a belt transfer member, to thereby form a full color image. Another method is a method where a recording medium is mechanically wrapped on a surface of a recording medium bearing member, which is disposed to face one latent electrostatic image bearing member, by electrostatic force or a gripper, and a series of the operations from the developing to transferring is repeated 4 times to thereby produce a full color image.
As an image forming method using an intermediate transfer member, proposed are a method where a full-color image forming apparatus equipped with a drum-shaped intermediate transfer member is used (see U.S. Pat. No. 5,187,526).
In these proposed methods, however, the visible image once transferred from the latent electrostatic image bearing member to the intermediate transfer member needs to be transferred again to a recording medium, and thus it is necessary to enhance transfer efficiency of the toner even higher than before.
Moreover, compared to the case of a single black color toner used in a monochrome photocopier, it is difficult to improve transfer efficiency of the color toners as an amount of the toners present on an intermediate transfer member is increased in a full color copier. Therefore, a 4-color visible image is not easily transferred uniformly, causing a partial transfer failure, so called a hollow defect.
In a transferring step, the recording medium and the intermediate transfer member are generally charged to have the opposite polarity to that of the toner, so that the toner is transferred by the electrostatic force.
During the transferring step of the toner with the electrostatic force, if transfer bias is increased to improve transfer efficiency of the toner, the charging amount of the toner is decreased, or is charged to have an opposite polarity by discharge occurred between the toner or latent electrostatic image bearing member and the recording medium (this may also referred to as “leak of toner charge” hereinafter). As a result of the leak of the toner charge, a phenomenon, so called retransfer, occur. This phenomenon is that the toner transferred to a recording medium moves back to the latent electrostatic image bearing member. Particularly in the case where the transferring step is performed a few times, as in the case of the aforementioned full-color image forming method, retransfer is more likely to occur with the toner which has been transferred earlier, and the retransfer of the toner results in formations of images with low image density. As the retransfer occur, unevenness is appeared in a resulting image. Therefore, high quality images cannot be formed.
In order to improve transfer efficiency of a toner, various methods for subjecting the toner to a treatment to give the toner mechanical impacts have been proposed (see JP-A Nos. 02-66559, 02-87159, 02-146557, 02-167566, and 05-61251).
As a result of these proposed methods, the transfer efficiency of the toner improves to some extent, but not to the sufficient level. Especially in the case of an image forming device using an intermediate transfer member, the transfer efficiency of such a toner is insufficient, and use of the toner does not give any effect in the prevention of the retransfer of the toner.
Moreover, for preventing the retransfer of the toner, proposed is a method for regulating a circularity distribution of the toner having a particle diameter of 3 μm or larger and having at least one endothermic peak in the temperature region of 120° C. as measured by differential scanning calorimetry (see JP-A No. 10-97095).
Moreover, it is disclosed that by controlling external additives contained in the toner having a certain circularity distribution and a certain weight average particle diameter to have the average particle diameter and shape factor within certain ranges on the toner particles, high quality images accurately reproducing minute dots can be attained, and the toner is not easily deteriorated by the high mechanical stress in a developing unit (see JP-A No. 11-174731).
The conventional art has not yet provided a toner having high transfer efficiency without causing retransferring, excellent low temperature fixing ability, and capable of forming high quality images, as well as providing a method for producing such a toner, and a developer and image forming method using such a toner. Therefore, it is currently strongly desired to promptly provide a toner having high transfer efficiency, excellent low temperature fixing ability, and capable of forming high quality images, as well as providing a method for producing such a toner, and a developer and image forming method using such a toner.